Liquid crystal display devices are provided in various devices, for example, a television device, a vehicle-mounted display such as a car navigation device, and mobile terminals such as a notebook personal computer, a tablet PC, a cell phone, and a smart phone.
Such liquid crystal display devices adopt various mode liquid crystals which are applied in accordance with purposes.
For example, in a vertical electric field type of liquid crystal display device such as a twisted nematic (TN) mode liquid crystal display device or an optically compensated bend (OCB) mode liquid crystal display device, an alignment direction of liquid crystal molecules included in a liquid crystal layer held between an upper substrate and a lower substrate is controlled by an electric field generated between a counter-electrode provided in the upper substrate and pixel electrodes provided in the lower substrate.
Furthermore, in a lateral electric field type of liquid crystal display device such as an in-plane switching (IPS) mode liquid crystal display device or a fringe-field switching (FFS) mode liquid crystal display device, a counter-electrode (referred to as a COM electrode in this type) and pixel electrodes are provided in the same substrate, and an alignment direction of liquid crystal display molecules included in a liquid crystal layer is controlled by an electric field (fringe electric field) generated between the counter-electrode and the pixel electrodes. The FFS mode liquid crystal display device can ensure a great aperture ratio, and thus has a high luminance and a good viewing angle characteristic.
It should be noted that a liquid crystal display device for use in a mobile terminal is strongly required to reduce the power consumption of a circuit, and a low-frequency driving method, an intermittent driving method, etc. are proposed as means for reducing the power consumption of the circuit. The low-frequency driving method is a method of reducing the power of the circuit by lowering a drive frequency of the liquid crystal display device to, e.g., ½ or ¼ of that under standard conditions. The intermittent driving method is a method of reducing the power of the circuit by stopping the circuit for a time period corresponding to several display time periods after writing is performed for a single display time period. In both those driving methods, a period of rewriting a video signal in a liquid crystal display unit is long. Thus, those driving methods are not suitable for displaying of moving images. However, they can be effectively applied, as methods for lowering the power of the circuit, to displaying of a still image or the like whose visibility is held in little account.
If the low-frequency driving method or the intermittent driving method is applied to a liquid crystal display device, it is necessary to reduce a flicker.
For example, in the case where a frame frequency was 60 Hz, which is applied in an ordinary liquid crystal display device, a flicker was not visibly recognized. On the other hand, in the case where the frame frequency was 20 Hz, which is ⅓ of 60 Hz, a flicker was visibly recognized. Furthermore, in the case where the frame frequency was further lowered, a flicker was more remarkably visibly recognized.